This is a break down of the symbols on the spawn and mini map along with the visuals on the map.
Here's a screenshot of the Spawn map with the symbols circled and numbered.
1. Regular sector, no special bonus.
2. Ammo sector, team controlling it can resupply restock bullets, grenades and HMG belts here by interacting with ammunition crates.
3. Key sector, this is has a high point value for the controlling team.
4. Recon sector, controlling team can use a field telephone to call in recon plane at a location of the users choice on the map.
5. Artillery sector, controlling team can use a field telephone to call in artillery at a location of the users choice on the map. Has a small chance at the start of the match to be Gas insted.
6. HQ, this is the starting point for each side. If cut off from any other controlled or neutral point it can be captured which ends the match. You can also restock bullets, grenades and HMG belts from the ammo crates here.
7. Is a HMG, any member of a squad can use these.